This invention relates to apparatus for use in the production of mouldings of a plastics material, such as polyurethane, which initially consists of at least two liquid components which have to be intimately mixed before introduction into a mould.
The proportions of the components in the mix must be carefully controlled and maintained constant if consistent results are to be obtained and this is made difficult since the viscosity of the components is dependent on temperature. If there is a temperature variation of any of the components the resulting changes in viscosity may not only upset the accuracy of metering of the components but can also produce pressure variations which may cause surging in the flow of the components to a mixing head and which in turn leads to a lack of coincidence at the beginning and end of each shot, thus producing incorrectly mixed material.
The maintenance of a sufficiently accurate temperature control involves the use of elaborate and expensive equipment and even so it is found that when using known apparatus temperature variations occur which make it impossible to produce moulded products of a consistently reliable and acceptable standard quality.
It will be understood that plastics materials of the kind used in the apparatus of this invention differ as regards the required working temperature. For example, one such material requires the components to be maintained at a temperature within the range 40.degree.-50.degree. C. whereas another material requires the components to be maintained at about ambient temperature. Accordingly, the maintenance of the components at constant temperature involves, in the first case, the supply of heat and, in the second case, probably the removal of heat.